There are two reasons to make moves at or before the July 31 trade deadline: One is that everyone else is doing it. The other is that it often works.

By “works,” we mean getting into a World Series. When the Tigers dealt prospect John Smoltz to Atlanta for Doyle Alexander in 1987, it didn’t work, except for the Braves of the 90s.

But the vast majority of minor league “prospects” are closer to the Costco loading dock than to Cooperstown.

Of the past 20 teams to play in a World Series, thirteen got a significant player at midseason. Only the 2011 Rangers gave up something valuable, when they included Chris Davis in the package that brought Koji Uehara from Baltimore.

It makes sense to deal at midseason because the selling teams, the ones out of contention, are desperate to unload high-paid players. During the off-season everyone is a hopeful 0-0.

And if the player is a rental property who can leave at season’s end, that is not always bad. The Angels were outraged after the 2008 season when Mark Teixeira, their summer prize, signed with the Yankees. They feel a little better now, since the compensatory pick for Teixeira became Mike Trout.

So far the Athletics gave the Cubs some of their highest-rated kids to get Jeff Samardzija and Jason Hammel. The Angels, who weren’t supposed to have hot prospects, gave up four to get closer Huston Street from San Diego. That was their third deal for a reliever, and suddenly their bullpen is no longer a greasy spot.

Brian Burke, the hockey executive, said the worst deals “are always made at the trade deadline.” He isn’t off-base, but recently the deals that keep you out of the World Series are the ones you don’t make.